Toward a Unified Theory of Narcosis: Brain Imaging Evidence for a Thalamocortical Switch as the Neurophysiologic Basis of Anesthetic-Induced Unconsciousness

A unifying theory of general anesthetic-induced unconsciousness must explain the common mechanism through which various anesthetic agents produce unconsciousness. Functional-brain-imaging data obtained from 11 volunteers during general anesthesia showed specific suppression of regional thalamic and...

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Bibliographic Details
Published in:Consciousness and cognition 2000-09, Vol.9 (3), p.370-386
Main Authors: Alkire, M.T., Haier, R.J., Fallon, J.H.
Format: Article
Language:English
Subjects:
Adolescent
Adult
Anesthesia, General
Anesthetics, Inhalation
brain imaging
Cerebral Cortex - drug effects
Cerebral Cortex - physiopathology
consciousness
corticothalamic
Energy Metabolism - drug effects
Energy Metabolism - physiology
Female
Fluorodeoxyglucose F18
Halothane
Humans
hyperpolarization
Isoflurane
Key Words: anesthesia
Male
mechanism
Mesencephalon - drug effects
Mesencephalon - physiopathology
Neural Pathways - drug effects
Neural Pathways - physiopathology
positron emission tomography
Reticular Formation - drug effects
Reticular Formation - physiopathology
sleep
thalamocortical
Thalamus - drug effects
Thalamus - physiopathology
Tomography, Emission-Computed
Unconsciousness - chemically induced
Unconsciousness - physiopathology
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Summary:A unifying theory of general anesthetic-induced unconsciousness must explain the common mechanism through which various anesthetic agents produce unconsciousness. Functional-brain-imaging data obtained from 11 volunteers during general anesthesia showed specific suppression of regional thalamic and midbrain reticular formation activity across two different commonly used volatile agents. These findings are discussed in relation to findings from sleep neurophysiology and the implications of this work for consciousness research. It is hypothesized that the essential common neurophysiologic mechanism underlying anesthetic-induced unconsciousness is, as with sleep-induced unconsciousness, a hyperpolarization block of thalamocortical neurons. A model of anesthetic-induced unconsciousness is introduced to explain how the plethora of effects anesthetics have on cellular functioning ultimately all converge on a single neuroanatomic/neurophysiologic system, thus providing for a unitary physiologic theory of narcosis related to consciousness.
ISSN:1053-8100
1090-2376
DOI:10.1006/ccog.1999.0423